/**
  * Read raw data from socket
  * @param int $length
  * @return string
  */
 protected function readRaw($length)
 {
     $data = '';
     $dataLeft = $length;
     do {
         $data .= $this->socket->read($dataLeft);
         $dataLeft = $length - strlen($data);
     } while ($dataLeft > 0);
     return $data;
 }